title: Synthesis and characterization of metallodendritic palladium-biscarbene complexes derived from 1,1'-methylenebis(1,2,4-triazole).
abstract: The syntheses of first generation dendritic compounds bearing 1,1'-alkane-1,1-diylbis(4-butyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene)palladium(II) dibromide on the periphery are described. The metallabiscarbene moieties have also been studied separately from the dendrimer. These compounds display a non-symmetric boat-to-boat conformational equilibrium that has axial and equatorial arrangements. The predominance of the axial conformer in the equilibrium is supported by DFT calculations. The X-ray solid state structures of axial conformers of 3-hydroxy- and 3-mesyloxy-1,1'-propane-1,1-diylbis(4-butyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene)palladium(II) dibromide are reported. These complexes display modest catalytic activity in the Heck reaction with activated aryl bromides and the dendritic catalysts were more active than the corresponding non-dendritic mononuclear species, a finding indicative of a cooperative effect.
authors.affiliation: Departamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de Química, Universidad de Castilla-La Mancha, Avda. Camilo José Cela, 10, E-13071, Ciudad Real, Spain.
authors.forename: Valentín
authors.initials: V
authors.lastname: Hornillos
authors.forename: Javier
authors.initials: J
authors.lastname: Guerra
authors.forename: Abel
authors.initials: A
authors.lastname: de Cózar
authors.forename: Pilar
authors.initials: P
authors.lastname: Prieto
authors.forename: Sonia
authors.initials: S
authors.lastname: Merino
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Maestro
authors.forename: Enrique
authors.initials: E
authors.lastname: Díez-Barra
authors.forename: Juan
authors.initials: J
authors.lastname: Tejeda
mesh_terms: D002384:Catalysis; D050091:Dendrimers / Q000737:chemistry*; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D014230:Triazoles / Q000737:chemistry*
chemical_list: C559538:1,1'-methylenebis(1,2,4-triazole); D050091:Dendrimers; D009942:Organometallic Compounds; D014230:Triazoles; C030011:carbene; D010165:Palladium; D008697:Methane